1. Field of the Invention
The present invention relates to a gateway unit used for connecting, for example, a public switched telephone network (PSTN) and an Internet protocol (IP) network with each other.
2. Description of the Related Art
In recent years, an information communication service including voice and data communication has become diversified. Resulting form this background, the number of carriers to newly enter a communication service field has increased and the intensity of service competition among carriers has increased. Such new carriers are called new common carriers (NCCs) and provide a variety of services by using a technique such as a voice over Internet protocol (VoIP). The VoIP is a technique to integrate a voice network and a data network by packetizing and transferring digital voice data.
In many cases, the NCCs are loaned facilities such as exchangers at a predetermined charge from a specific carrier already having a subscriber line. Many of the NCCs construct their own exchange networks such as IP networks by their own funds. The NCCs form communication systems by adding a PSTN of the specific carrier. These facilities are utilized in a compound manner for providing services to public users.
A gateway unit is used for connecting different communication networks such as the PSTN and the IP network with each other. This kind of gateway unit has an IP conversion unit for converting voice data and binary data into an IP packet and a packet switching unit for switching the IP packet. An example of this kind of gateway unit is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-205831. This document discloses a button telephone main apparatus as an example of the gateway unit. This document also discloses a system formed by a bus topology. The information communication in the bus topology becomes half double communication.
By the way, an internal control system in this kind of gateway unit is often a unique system at every gateway unit vender and a low-speed transmission system such as serial transmission. The low speed of a data transmission speed inside the gateway unit causes the performance of processing to notify, for example, failure information to an external network managing device to deteriorate. In this case, the gateway unit makes the response of the network management slow in speed. In many cases, the gateway unit and a network management device to manage it are connected through the IP. Thereby, the adaptation of the unique system for the internal control system requires protocol conversion processing and makes the response of the network management further slow in speed.